1. Field of the Invention
The invention relates to an injection molding apparatus comprising a stack mold with two outer mold portions enclosing a center platen between them, the center platen on two sides thereof, together with the mold portions, defining hollow form cavities and having a connector opening and feed ducts therein, a drive-and-close unit being provided for effecting a relative displacement between the mold portions and the center platen for opening and closing, respectively, the hollow form cavities, and an injection molding device being adapted for connection to the connector opening, the injection molding device remaining connected to the connector opening during the relative displacement between the mold portions and the center platen.
2. Description of the Related Art
An injection molding apparatus of the afore-mentioned kind has been known from JP-U2 62-18418.
The prior art injection molding machine is provided with a stack mold having a center platen and one outer mold portion being displaceable whereas the other mold portion is stationary. By means of a first piston-cylinder-unit the displaceable mold portion may be displaced. The displaceable mold portion is provided with a spur rack, meshing with a pinion being rotatably journalled on the center platen. The stationary mold portion, too, is provided with a spur rack which, too, meshes with the pinion being journalled on the center platen. By means of this gear one can, therefore, continuously close the entire stack mold during displacement of the displaceable mold portion because due to the action of the gear the center platen will be displaced with half the velocity, as compared with the displaceable mold portion.
In the prior art injection molding machine the injection molding device is arranged besides the stationary mold portion on that side being opposite to the center platen. The injection molding device is arranged on a carriage and can, therefore, be displaced in the same direction as the displaceable mold portion and the center platen. The carriage is provided with a second piston-cylinder-unit. The cylinder of the latter is rigidly connected with the carriage of the injection molding device whereas the piston rod is rigidly connected with the stationary mold portion. A piston on the piston rod is designed double-acting with the effective surface areas on both sides of the piston being differently sized. In this way the injection molding device can be displaced relative to the stationary mold portion.
The injection molding device is connected to the center platen by means of an elongate injection cylinder which extends through a through opening in the stationary mold portion. An injection cylinder mouthpiece is pressed against an input opening of the center platen. The pressure exerted on the mouthpiece may be predetermined by means of the second piston-cylinder-unit.
When the stack mold is opened by actuating the first piston-cylinder-unit, one may appropriately control the second piston-cylinder-unit such that the injection molding device follows the center platen during the displacement of the latter so that the injection cylinder mouthpiece will remain in contact on the input connector opening of the center platen.
In this way the injection molding device together with the center platen are a unit that is not separated during the opening and the closing displacement of the stack mold. The required reaction forces between the center platen and the injection molding device are supported by a building base, on the one hand from the center platen via the pinion, the spur rack, the displaceable mold portion and the first piston-cylinder-unit and, on the other hand, via the injection molding device, its carriage, cylinder, piston, piston rod and the stationary mold portion.
The prior art injection molding machine has the disadvantage that substantial pressures that have to be effected between the injection molding device mouthpiece and the center platen have to be supported by the base of the injection molding machine over this very complicated path of travel. Another disadvantage of the prior art machine tool is that the injection molding device must constantly follow the center platen due to the aforedescribed hinematics of the machine by supporting the second piston-cylinder-unit on the stationary mold portion via a continuous control and actuation of the second piston-cylinder-unit. Therefore, it is mandatory to constantly control the pressure within the second piston-cylinder-unit, i.e. during each displacement for opening and for closing, respectively, of the stack mold. This requires a relatively complicated control and may be the cause for failures, in particular due to leaks in the piston-cylinder-units that are constantly in action.